Common Names

Ngaio mirid

Biostatus and Distribution

This endemic mirid is found throughout New Zealand on its host plant, ngaio, Myoporum laetum (Myporaceae). Both the nymphs and adults feed on young leaves and stems. The mirid occurs in city gardens and parks as well as native ecosystems.

Conservation status: Widespread, not threatened.

Life Stages and Annual Cycle

In Auckland, adults and nymphs can be found at all times of the year, where there may be three or more overlapping generations. There are likely to be fewer generations in cooler parts of the country.

Adults are found on shoots with young leaves. They often hide on the other side of a leaf or stem. They are mottled brown. The female has an ovipositor, at the tip of her abdomen that is used to insert eggs into leaves or young stems.

Nymphs hatch from the eggs. There are five nymphal stages, each is called an instar. Nymphs go from one stage to the next by moulting (changing their skin). During moulting, the skin on the dorsal side splits and the next stage pulls itself out of the old skin. First instar nymphs are like small, green, wingless adults. As the insects progress through the nymphal stages, the colour remains predominately green. The third instar has small wing buds and only those of the forewing are visible. In the fourth and fifth instars both pairs of wing buds are visible and tend to be darker green in colour. They are largest in the 5th instar. Adults emerge from fifth instar nymphs.

Walking and flying Nymphs and adults have three pairs of legs. Adults have two pairs of wings, the front chitinised pair covering the membranous hind wings when not flying. Most of the forewing is opaque mottled brown, the rest is membranous.

Feeding Like other Hemiptera, the ngaio mirid has piercing and sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. When it wishes to feed the bug moves the tip of the rostrum to a suitable part of the plant. The stylets are then gradually pushed into the plant. The stylets form two tubes, one through which saliva is injected into the plant and a second through which plant juices are sucked up into the insect. Ngaio mirid feeding has not been studied, but the damage to leaves show that they feed on the cells in the leaf and from one point of insertion of the stylets, can reach in all directions forming a ‘star-like’ pattern of pale, damaged tissue. They probably use their saliva to digest the plant cells.

Recognition

The ngaio mirid is the only mirid that breeds on ngaio, Myoporum laetum (Myoporaceae). However, another hemipteran, the Yellow Australasian leafhopper, Anzygina zealandica (Hemiptera: Cicadellidae), also causes yellowing of ngaio leaves. The two insects and their damage can be distinguished by the following.

The adult ngaio mirid is mottled brown, whereas the adult Yellow Australasian leafhopper is smaller, narrower, and yellow-green. The nymphs of both species are green. Nymphs of the ngaio mirid are agile and often run to the other side of a stem or leaf when disturbed. The Yellow Australasian leafhopper nymphs are more slender and, like the adults, tend to move sideways. The ngaio mirid is the only mirid that breeds on ngaio, Myoporum laetum (Myoporaceae). Feeding by both the mirid and the leafhopper insects causes yellow areas on the leaves, but only the ngaio mirid makes black faecal deposits on the underside of the leaves.

Natural Enemies

No natural enemies of the ngaio mirid are known. They may be caught by birds, spiders and predatory insects.

Host Plants

The ngaio mirid lives and breeds on the New Zealand endemic tree, ngaio, Myoporum laetum Forst. f. (Myoporaceae). The species has been found feeding on hybrids between ngaio and the Australian species, Myoporum insulare R.Br., but does not appear to feed and breed on the Australian species. Adults and juveniles feed by inserting the stylets into plant leaves and perhaps young stems. It is assumed that they inject saliva into plant cells and suck up predigested or partly digested cell contents from the leaves.

Control

Normally, mirid damage to ngaio trees does not cause trees any significant harm. However, extensive damage to leaves of ngaio trees can occur. Nothing is known about its natural control. If there is concern about the damage to a young tree, application of a non-persistent insecticide to all the leaves on the tree may help.

Additional Information

Damage to other plants by Chinamiris miridsSeveral different species of Chinamiris mirids live on native ornamental shrubs in gardens and plant nurseries. Sometimes they cause obvious damage to these plants.

Mirid opportunistsMirids are opportunists (Wheeler 2001) and it is possible that this mirid will prey on aphids and other small insects on its host plant..